Environmental Simulations for EOD Shaped Charges

by Reto Liechti [ Saab Bofors Dynamics Switzerland, Ltd. ] - view pdf

This article describes the methodology and importance of environmental simulations and testing of shaped charges used for the disposal of explosive remnants of war and landmines. The author discusses a single sequence of tests conducted on a specific product as an example of the depth to which environmental factors should be investigated in order to address them before final production and manufacture.

Vibration caused by transportation, temperature changes and the natural aging process, as well as other environmental factors, can impact the safe operation of a product. Assessing environmental effects on a product can be time-consuming and expensive. However, in the case of explosive ordnance-disposal equipment, environmental simulations and testing are basic tools for the scientific investigation and production of safe new products.

Image 1. Rain plant setup. All photos © Saab Bofors Dynamics Switzerland Ltd.
Figure 1. Diagram of development phases.
All graphics © Saab Bofors Dynamics Switzerland Ltd.

The Need for Environmental Simulations

When handling explosives, safety and reliability are key factors for a successful mission. In demining operations with in situ disposal, shaped charges are often used, especially when inducing deflagration of submunitions (cluster bomblets). Thus, using shaped charges speeds up operations and minimizes hazardous risks to deminers.

Image 1. Rain plant setup. All photos © Saab Bofors Dynamics Switzerland Ltd.
Figure 2 .Example of a test program.

Many shaped charges are available on the market. Any of these charges used in the field can cause harm if not used properly. The shaped charges referred to in this article are proven through a program of extensive environmental tests, not only in their development phase but also throughout the manufacturing stage. These environmental test programs include assessment, clearance checks (to ensure operators can handle them) and transport-vibration checks (to test for worst-case land, sea and air conditions). Environmental tests also consider extreme environmental aggression such as rapid and extensive changes in temperature, pressure, humidity and adverse immersion environments such as sand, dust storms and water. These tests guarantee the product can withstand different circumstances and provide full performance until the end of its anticipated life cycle.

Development Phase

Environmental simulations are often performed either before a product is in its early development phase or when a product is about to enter the market and go into service. Development phases are usually detailed programs with a number of activities and individual phases that some countries refer to as a series of Design Definitions. The content for each DD phase varies from one project to another but generally takes the form as illustrated in Figure 1.

Test Program

A test program can be performed with many individual and independent experiments that focus on individual test events. These tests do not represent real circumstances, and therefore a test program combines a variety of tests and possible scenarios either in parallel (each test performed independently) or in a sequence. Combinations are the most common and realistic approach. Figure 2 shows six typical test sequences which are performed in parallel for the SM-EOD 331 explosive shaped charges. Each sequence can vary in the number of tests, and this example shows one or two tests in each sequence followed by an X-ray inspection and a static detonation at the end of each sequence.

Image 1. Rain plant setup. All photos © Saab Bofors Dynamics Switzerland Ltd.
Figure 3. Single sequence of test program.

Sequence

In order to discuss a sequence for environmental testing, one sequence of the tests will be more closely examined now. Each test is dependent on its predecessor. With this dependence, potential failures can be summed; this summation results in better estimates than the product's mechanical limit of the product (see Figure 3).

Standards and Specifications

All tests should be according to certain test-method type standards such as:

Vibration Test

High-cycle fatigue materials performance8 is commonly characterized by an S-N curve (S = stress, N = cycles to failure), also known as a Wöhler-curve. A vibration test simulates the effect with vibrations often experienced during transportation and operation. The test attempts to cover all occurrences the product will encounter during its product life cycle. In the case of explosive charges, the more intense the vibration environment, the faster the aging process occurs and the higher the possibility of discovering cracks and gaps in between the explosive filling and the mechanical body.

X-ray inspection will prove if the vibration tests had any influence (see Figure 3). In this illustrative example, the procedure is undertaken according to MIL STD 810E, method 514.4, category one (basic transportation) with the following characteristics:

Vibration test specifications.

Configuration

Products in original packaging

Vibrator V 964

Horizontal, transversal and vertical axis vibrations

Frequency

10 - 500 Hz/1.04 g

Testing time

1 h per axis (3 axis)

MIL STD

MIL STD 810E, Meth. 514.4, Fig. 514.4 -1

Number of test pieces

n = 30 – batch no. 2050 – 2079

Packing

Wooden box no. 047 with polystyrene-foam

Temperature

Room temperature

Image 1. Rain plant setup. All photos © Saab Bofors Dynamics Switzerland Ltd.Image 1. Rain plant setup.
All photos © Saab Bofors Dynamics Switzerland Ltd.

Rain Test

The rain test simulates a strong rainfall on the field. In this illustrative example, a method of a 360-degree rain toward the product with specific intensity for a certain time was chosen. The details are as follows:

Image 2. Rain plant setup.Image 2. Rain plant setup.

Rainfall test specifications.

Test order-No.

4182 09682 and 4185 09690

Used facility

Rain plant No. 80

Frequency

10 - 500 Hz/1.04 g

Type of test

Rain test unpacked

MIL STD

According to 810D, meth. 506.2

Rain quantity

100 mm/h, wind velocity 18 m/s

Duration

30 min.

Rotary table

Turning

The rain test determines the effectiveness of seals and cases in preventing water penetration. The test also shows the product capability to satisfy performance during and after exposure to water.

X-ray Inspection

An X-ray inspection is performed after each individual environmental test in a sequence. It is a real-time nondestructive subsurface inspection and shows the product's internal characteristics. The inspection is a dynamic 360-degree live image where the object is rotated in front of the X-ray source. During a visual inspection by trained operators, the X-ray will indicate any hairline cracks or air gaps.

Image 3. Dynamic X-ray inspection.Image 3. Dynamic X-ray inspection.
Image 4. Penetration performance witness.Image 4. Penetration performance witness.
Image 5. Penetration performance witness.Image 5. Penetration performance witness.

The advantage of the X-ray inspection is that no harm will reach the product, but it will provide full information about the object's density, which is directly linked to quality and performance. Any cracks or gaps detected would expectedly have a negative impact on product performance and accuracy.

Performance Test

In addition to all previous tests, a final performance test simulates a mine or unexploded ordnance-disposal operation where, for instance, a mine body or artillery shell requires penetration before deflagration or detonation. The setup for such a performance test with a defined target can utilize multiple rolled homogenous armor plates as shown in the Images 4 and 5.9 The penetration will show any performance problems such as variation, dispersion or inadequate penetration of the jet's tip that may not be detectable in any of the previous tests. The requirements for the performance penetration test are that it must be reproducible and permit comparisons to identify penetration performance, which is the most important testimony of a high-quality product. In the field, high accuracy and reproducibility will permit fast intervention and safe and successful operations.

Performance test specifications.

Test order-No.

33, charge 18

Used facility

Bunker No. 3

Type of test

Rain test unpacked

Test temperature

+ 7° C (44° F)

 

Additional Tests

In addition to the tests described above, the SM-EOD 33 products are subject to:

Independence

Environmental simulation and testing can have a higher credibility if a neutral, independent company performs the testing and analysis. An external laboratory without any affiliations to the supplier is common. However, not all laboratories can undertake tests with explosives, which in the case of explosive products, limits the number of test suppliers available.

Image 1. Rain plant setup. All photos © Saab Bofors Dynamics Switzerland Ltd.
Figure 4. Protocol of vibration test. The test verifies whether the product will funtion and withstand the anticipated vibration exposures throughout its lifecycle.

Conclusion

This article discusses a single sequence of tests conducted on a specific product as an example of the depth to which environmental factors should be investigated in order to address life-cycle problems before final production and manufacture.

In the early development phase of most products, environmental simulations and testing can uncover potential future risks and reduce the eventual time to market. Simulations and testing can improve designs and ensure the product is safe and reliable throughout its full life cycle. These environmental assessments can be time-consuming and expensive, but assessment prior to product use in the field is more economical and ethical than marketing untested products that may result in considerable damages and loss of life.

 

Biographies

Reto LiechtiReto Liechti is Area Sales and Product Manager at SAAB Bofors Dynamics Switzerland, responsible for SM-EOD demining systems. He holds a Bachelor of Applied Science in Management at European Business School Thun, and was previously Project and Product Manager for a mechanical engineering firm.


Contact Information

Reto Liechti
Area Sales Manager/Product Manager
SAAB Bofors Dynamics Switzerland Ltd
Allmendstrasse 86
3602 Thun / Switzerland
Tel: +41 332 282 063
Fax: +41 332 282 791
Mobile: +41 799 064 660
Email: reto.liechti@saabgroup.com
Website: http://saabgroup.com/sm-eod

 

Endnotes

  1. "SM-EOD 33 Contact Free Demining Equipment." SAAB Bofors Dynamics Switzerland Ltd. http://saabgroup.com/sm-eod. Accessed 6 June 2012.
  2. "Department of Defense Test Method Standard MIL STD 810F: Environmental Engineering Considerations and Laboratory Tests." Department of Defense. 1 January 2000. MIL STD 810F emphasizes tailoring the equipment's environmental design and test limits to the conditions that it will experience throughout its service life, and establishing test methods that replicate the effects of environments on the equipment rather than imitating the environments themselves.
  3. "Department of Defense Test Method Standard MIL STD 331C: Fuze and Fuze Components, Environmental and Performance Tests." Department of Defense. 5 January 2005. MIL STD 331C reflects standardization among the services and improvements in fuze design, test technology, and safety.
  4. "Standardization Agreement for Environmental Testing Edition 2." North Atlantic Treaty Organization Standardization Agency. 19 April 2005. STANAG 4370 gives guidelines on the management of environmental testing of defense material, characterizes environments, and standardizes environmental testing processes.
  5. "Allied Environmental Conditions and Test Publications 300: Climactic Environmental Tests Edition 3." North Atlantic Treaty Organization Standardization Agency. 18 May 2006. AECTP 300 is one of 5 documents included in STANAG 4370. AECTP 300 test methods address climatic elements which may occur either individually or in combination with other climatic elements or mechanical environments.
  6. "Allied Environmental Conditions and Test Publications 400: Mechanical Environmental Tests Edition 3." North Atlantic Treaty Organization Standardization Agency. 18 May 2006. AECTP 400 Test Methods address mechanical environments, both individually and when combined with other environments, such as climatic environments included in AECTP 300. The application of combined environments is relevant and often necessary where failures could be expected from potential synergistic effects.
  7. "International Electrotechnical Commission 60068-2: Environmental Testing." International Electrotechnical Commission. October 1988. IEC 60068-2 enumerates a series of environmental tests and appropriate severities, and prescribes various atmospheric conditions for measurements for the ability of specimens to perform under normal conditions of transportation, storage and operational use.
  8. The likelihood that a material will break down (fatigue) over multiple uses (cycles).
  9. Rolled Homogenous Armor is a type of steel used to armor vehicles from velocity metal projectiles. It is made by processing cast steel billets and then rolling them into plates. Hot rolling homogenizes the structure of the steel elongates the grain structure, thus strengthening the steel and allowing stress to be loaded throughout the metal instead of concentrating on one area.

 

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